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Antlion's pits

Myrmeleontidae

Description:

An average-sized larva digs a pit about 2 inches (5 cm) deep and 3 inches (7.5 cm) wide at the edge. This behavior has also been observed in a family of flies, the Vermileonidae, whose larvae dig the same sort of pit to feed on ants. Having marked out the chosen site by a circular groove, the antlion larva starts to crawl backwards, using its abdomen as a plough to shovel up the soil. By the aid of one front leg it places consecutive heaps of loosened particles upon its head, then with a smart jerk throws each little pile clear of the scene of operations. Proceeding thus it gradually works its way from the circumference towards the center. As it slowly moves round and round, the pit gradually gets deeper and deeper, until the slope angle reaches the critical angle of repose (that is, the steepest angle the sand can maintain, where it is on the verge of collapse from slight disturbance). When the pit is completed, the larva settles down at the bottom, buried in the soil with only the jaws projecting above the surface, often in a wide-opened position on either side of the very tip of the cone. Since the sides of the pit consist of loose sand at its angle of repose,[10] they afford an insecure foothold to any small insects that inadvertently venture over the edge, such as ants. Slipping to the bottom, the prey is immediately seized by the lurking antlion; or if it attempts to scramble up the treacherous walls of the pit, it is speedily checked in its efforts and brought down by showers of loose sand which are thrown at it from below by the larva. By throwing up loose sand from the bottom of the pit, the larva also undermines the sides of the pit, causing them to collapse and bring the prey with them. Thus it does not matter whether the larva actually strikes the prey with the sand showers. Antlion larvae are capable of capturing and killing a variety of insects and other arthropods, and can even subdue small spiders. The projections in the jaws of the larva are hollow and through this the larva will suck the fluids out of its victim. After the contents are consumed, the dry carcass is flicked out of the pit. The larva readies the pit once again by throwing out collapsed material from the center, steepening the pit walls to the angle of repose.

Habitat:

Antlions are especially abundant in soft sand beneath trees or under overhanging rocks. Apparently the larvae prefer dry places that are protected from the rain.

Notes:

When it first hatches, the tiny larva specializes in very small insects, but as it grows larger, it constructs larger pits and thus catches larger prey. Eventually the larva attains its maximum size and undergoes metamorphosis. The entire length of time from egg-laying to adulthood may take two or three years due to the uncertainty and irregular nature of its food supply.

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valentinezza
Spotted by
valentinezza

Sant'Olcese, LIG, Italy

Spotted on Aug 27, 2013
Submitted on Aug 27, 2013

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Reference

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